My guess is that Tyrion and Sansa eventually fall in love.
Jon Snow will defeat the white walker invasion with the help of Tyrion and Sansa and Deaneries.
Daeneries will go back and rule the foreign lands she first conquered, John Snow will Rule region north of the wall.
And what’s going on with the young Stark kid and that golden tree? Such a big build up to getting there, then nothing.
Maybe in the book Sansa has some power left. Not in the HBO Series. She is so much damaged goods now that Littlefinger betrayed her to Ramsey.
That did not happen in the books, and just should never have happened in the series.
The only plausible scenario to resurrect it is as you have described... She reunites with Tyrion.
Haven't watched the show but in the book Tyrion is totally scarred and has lost his nose. Probably not Sansa's cup of tea.
That Tyrion might become king from the Lannister connections and as legal husband of Queen of the North, uniting the Kingdoms.
Or exits as King of the North with Sansa while Jon Snow and Daenerys marry to bring peace. Jon = ice + Daenerys = fire even meets the title.
And because Daenerys can’t have kids, Sansa rules over winterfell for their lifetime, and as Jon’s closest legal heir, her kids are princes and princesses of the north and the Iron Throne.